Cable television receivers typically need to deal concurrently with reception of around 6 channels, some of which may be for video signals and others for data signals. These requirements are likely to increase in future, in order to meet increasing data bandwidth requirements and multiple video signals for distribution via a ‘home gateway’ modem. This may, for example, necessitate the concurrent reception of 12 or more channels located anywhere in a 1 GHz bandwidth. FIG. 1 illustrates schematically a possible location of 12 wanted channels 101 selected out of a number of available channels 102 over a bandwidth from 50 MHz to 1 GHz. The 12 channels may, for example, represent 8 channels for high-speed internet and 4 video channels.
Depending on frequency planning by the operator of the cable service (which may be a multiple system operator, or MSO), the lower part of the spectrum (for example 50 MHz to 550 MHz) may be occupied with analogue channels, while the upper part of the spectrum (550 MHz to 1 GHz) may be reserve for digital channels and data. The concurrent reception of several channels may therefore be limited to the 550 MHz-1 GHz band only.
Using traditional single-channel receiver techniques, concurrent reception of 12 channels would require 12 single-channel receivers, which leads to an unacceptably high cost system solution.
Therefore, there is a current interest in developing broadband receivers that allow for the concurrent reception of a number of channels.
A wideband analog to digital converter (ADC) may be used to convert the whole 1 GHz RF input signal, allowing selection of individual channels to be carried out in the digital domain. However, wideband ADCs are difficult to implement, particularly over such a large bandwidth, and may have a limited dynamic range.
A possible solution is to split the input signal bandwidth into multiple smaller bandwidths, as for example disclosed in WO 2007/145637, in which multiple amplifier-filter circuits are configured to receive and separate a multichannel RF input signal into corresponding analog signals in different frequency bands. Multiple ADCs are provided for converting each analog signal into a digital signal. This type of solution is illustrated schematically in FIG. 2, in which a single wideband low noise amplifier (LNA) 201 provides an amplified RF signal to multiple filters 2021-202N and multiple sub-band receivers 2031-203N. This type of solution, however, requires the use of multiple ADCs, so that each ADC has only a limited portion of the input bandwidth to process, and uses multiple amplifiers and filters, thereby increasing the complexity of the receiver. The issue of dynamic range of each ADC is also not considered.
It is an object of the invention to address one or more of the above mentioned problems.